I had 2 bare backed girls last winter....and it was frigid, like way below freezing frigid, for weeks....they were fine.
You can use a heat lamp but they are very dangerous, can cause other problems and plenty of birds are fine without them.
A higher protein feed is good for molters for sure.
I like to feed an 'all flock' 20% protein crumble to all ages and genders, as non-layers(chicks, males and all molting birds) do not need the extra calcium that is in layer feed and chicks and molters can use the extra protein. Makes life much simpler to store and distribute one type of chow that everyone can eat and have calcium available at all times for the layers, oyster shell mixed with rinsed, dried, crushed chicken egg shells in a separate container.
The higher protein crumble offsets the 8% protein scratch grains and other kitchen/garden scraps I like to offer.